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Aggregation-enhanced luminescence and vibronic coupling of silole molecules from first principles
Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing.
Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing.
Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing.
Department of Chemistry, Beijing Normal University.
Show others and affiliations
2006 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 73, no 20, 205409- p.Article in journal (Refereed) Published
Abstract [en]

Aggregate formation in molecular solids usually quenches the luminescence, a piece of bad news for molecular electronic devices. However, siloles present extremely high luminescent efficiency in solid state as well as in aggregation, but have almost no luminescence in solution. By employing a first-principles calculation to study excited states and vibronic couplings, we find that it is the low-frequency twisting motions of side rings which enhance the nonradiative decay. These motions can be suppressed either by solid-state packing, by aggregation formation in polar solvents, or by increasing the solvent viscosity; thereby, the radiative decay becomes dominant, resulting in peculiar aggregate-induced emission phenomena in siloles.

Place, publisher, year, edition, pages
2006. Vol. 73, no 20, 205409- p.
Keyword [en]
RESTRICTED INTRAMOLECULAR ROTATION; LIGHT-EMITTING-DIODES; THERMAL-STABILITY; INDUCED EMISSION; 2, 3, 4, 5-TETRAPHENYLSILOLES; PHOTOLUMINESCENCE; POLYMERS; STATES
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6978DOI: 10.1103/PhysRevB.73.205409ISI: 000237950500092Scopus ID: 2-s2.0-33646570891OAI: oai:DiVA.org:kth-6978DiVA: diva2:11843
Note
QC 20100820Available from: 2007-04-16 Created: 2007-04-16 Last updated: 2010-08-20Bibliographically approved
In thesis
1. Theoretical Design of Molecular Photonic Materials
Open this publication in new window or tab >>Theoretical Design of Molecular Photonic Materials
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents a theoretical study on optical properties of molecular materials. Special emphasis has been put on the influence of solvent environment, nuclear vibrations, and aggregation effects on molecular properties like linear and nonlinear polarizabilities, one- and two-photon absorption probabilities. All calculations have been performed by means of time independent and dependent quantum chemical methods at the Hartree-Fock and density functional theory levels. Solvation models that include both long range and short range interactions have been employed for calculations of optical properties of molecules in solutions. Pure vibrational and zero-point vibrationally averaged contributions have been taken into account for linear and nonlinear polarizabilities. The linear coupling model is applied to simulate vibronic profiles of optical absorption spectra. The computational strategies described in this thesis are very useful for the design of efficient molecular photonic materials.

More specifically, the nonmonotonic behavior of the solvatochromic shifts and the first hyperpolarizability of para-nitroaniline (pNA) with respect to the polarity of the solvents have been theoretically confirmed for the first time. The significant contributions of the hydrogen bonding on the electronic structures of pNA are revealed. Vibrational contributions to the linear and nonlinear polarizabilities of methanol, ethanol and propanol have been calculated both at the static limit and in dynamic optical processes. The importance of vibrational contributions to certain nonlinear optical processes have been demonstrated. A series of end-capped triply branched dendritic chromophores have been studied with the result that their second order nonlinear optical properties are found strongly dependent on the mutual orientations of the three chromophores, numbers of caps and the conjugation length of the chromophores. Several possible mechanisms for the origin of the Q-band splitting of aluminum phthalocyanine chloride have been examined. Calculated vibronic one-photon absorption profiles of two molecular systems are found to be in very good agreement with the corresponding experiments, allowing to provide proper assignments for different spectral features. Furthermore, effects of vibronic coupling in the nonradiative decay processes have been considered which helps to understand the aggregation enhanced luminescence of silole molecules. The study of molecular aggregation effects on two-photon absorption cross sections of octupolar molecules has highlighted the need to use a hybrid method that combines density functional response theory and molecular dynamics simulations for the design of molecular materials.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 52 p.
Series
Trita-TEC-PHD, ISSN 1653-4468
Keyword
Optical property, Molecular material, Solvent environment, Nuclear vibrations, Aggregation effect
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-4333 (URN)978-91-7178-619-7 (ISBN)
Public defence
2007-04-27, FA32, Roslagstullsbacken 21, AlbaNova University Center, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100820Available from: 2007-04-16 Created: 2007-04-16 Last updated: 2010-08-20Bibliographically approved

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